The present invention relates to a liquid crystalline compound and a liquid crystal composition. More specifically, it relates to a novel liquid crystalline compound which has a hetero ring structure and which has a difluorovinyl group at a terminal of the compound, a liquid crystal composition comprising the same, a liquid crystal display which is constituted with this liquid crystal composition and a synthetic intermediate for the liquid crystalline compound. In the present invention, the term of the liquid crystalline compound is used as a general term of a compound showing a liquid crystal phase and a compound that does not show a liquid crystal phase but is useful as a structural component for a liquid crystal composition.
Many display elements making use of characteristics of a nematic liquid crystal compound have so far been produced. In recent years, a liquid crystal display (LCD) is widely used for various uses including not only watches and portable electric calculators but also monitors for personal computers and portable telephones, and demand therefor has been growing large year by year. In accordance with it, improvement items for performances required for LCD have come to extend over many divergences such as an expansion in an operable temperature range, a shift to high density and coloring of the display, an acceleration in response and an expansion in a viewing angle. It is known that various display modes using electro-optical effects, such as a DS (dynamic scattering) mode, a TN (twist nematic) mode, a GH (guest host) mode, an STN (super twist nematic) mode, an IPS (in-plane switching) mode and a VA (vertical alignment) mode have been proposed in order as means for solving them.
In such situation, various characteristics are required to a liquid crystal composition used for LCD according to the respective display modes. First, the physical property values such as optical anisotropy (xcex94n), dielectric anisotropy (xcex94xcex5), viscosity (xcex7), conductivity and elastic constant ratio K33/K11 (K33: bend elastic constant and K11: spray elastic constant) of a liquid crystal composition are required to have values which are optimum for a display mode and a form of an element. In LCD may be used in outdoor at low temperature as a portable telephone and a mobile personal computer, a liquid crystal composition that is stably operated at low temperature is required. In order to meet this, a liquid crystalline compound constituting it has to be excellent in solubility at low temperature. Further, a portable telephone tends to be always increased, though it has a small display, in an information amount displayed thereon, so that display having high contrast is desired. In an STN mode that is mainly used for the LCD, a liquid crystalline compound having a high K33/K11 value is required in order to obtain high contrast ratio. Further, in order to achieve quick response in any of the LCD""s shown above, a liquid crystal composition having low viscosity is required, and a liquid crystalline compound has to be indispensably reduced as well in viscosity. In addition thereto, given as common items of characteristics required to a liquid crystal composition are stability against moisture, light, heat and air that are usually present under use environment and stability against an electric field and electromagnetic irradiation. Further, the respective components of a liquid crystalline compound constituting a liquid crystal composition have to be chemically stable to each other in a use environment, and it is important as well that they have good solubility with each other.
In the existing state, however, it is very difficult to solve these problems only with the existing liquid crystal compounds and liquid crystal compositions, and it is an urgent matter to develop a novel liquid crystalline compound and liquid crystal composition which can meet the various requirements described above.
An object of the present invention is to provide a liquid crystalline compound which has particularly a wide liquid crystal phase temperature range, low viscosity, a large elastic constant ratio K33/K11 and solubility improved at low temperature so that the problems of conventional techniques can be overcome, a liquid crystal composition comprising the same, a liquid crystal display which is constituted with the above liquid crystal composition and an intermediate useful for producing the liquid crystalline compound having excellent characteristics.
In order to achieve the objects described above, the following inventions are claimed for the grant of a patent in the present application.
(1) A difluorovinyl compound represented by Formula (1): 
wherein Y1 represents H or straight chain or branched alkyl group having 1 to 10 carbon atoms, and optional xe2x80x94CH2xe2x80x94 in the above alkyl group may be replaced by xe2x80x94Oxe2x80x94 or xe2x80x94CHxe2x95x90CHxe2x80x94, but xe2x80x94Oxe2x80x94 is not adjacent to each other, and at least one H in Y1 may be substituted with halogen or a cyano group; A1, A2, A3 and A4 each independently represent 1,4-cyclohexylene in which optional xe2x80x94CH2xe2x80x94 which is not adjacent to each other may be replaced by xe2x80x94Oxe2x80x94, 1,4-phenylene in which optional H may be substituted with halogen, and a single bond, in which at least two of A1, A2, A3 and A4 have the ring structure described above, and at least one of them is 1,4-cyclohexylene in which xe2x80x94CH2xe2x80x94 is replaced by xe2x80x94Oxe2x80x94; Z1, Z2 and Z3 each independently represent a single bond, xe2x80x94(CH2)2xe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94(CH2)4xe2x80x94, xe2x80x94O(CH2)3xe2x80x94 or xe2x80x94(CH2)3Oxe2x80x94; n represents 0 or an integer of 1 to 10, provided that when any of A1, A2, A3 and A4 is 1,4-phenylene, Z1, Z2 and Z3 are single bonds, and among them, when A1 is 1,3-dioxane-2,5-diyl and A2 is 1,4-phenylene and when A3 is 4,cyclohexylene and A4 is a single bond, Y1 is H, and n is not 0.
(2) A difluorovinyl compound as described in the above item [1], wherein A1, A2, A3 and A4 each independently represent 1,4-cyclohexylene in which optional xe2x80x94CH2xe2x80x94 which is not adjacent to each other may be replaced by xe2x80x94Oxe2x80x94, 1,4-phenylene and a single bond, in which at least two of A1, A2, A3 and A4 have the ring structure described above, and at least one of them is 1,4-cyclohexylene in which xe2x80x94CH2xe2x80x94 is replaced by xe2x80x94Oxe2x80x94; Z1, Z2 and Z3 each independently represent a single bond, xe2x80x94(CH2)2xe2x80x94 or xe2x80x94(CH2)4xe2x80x94, provided that when any of A1, A2, A3 and A4 is 1,4-phenylene, Z1, Z2 and Z3 are single bonds, and among them, when A1 is 1,3-dioxane-2,5-diyl and A2 is 1,4-phenylene and when A3 is 1,4-cyclohexylene and A4 is a single bond, Y1 is H, and n is not 0.
(3) A difluorovinyl compound as described in the above item (1), wherein A1 is 1,3-dioxane-2,5-diyl; A2 is 1,4-cyclohexylene; and A3, A4, Z1, Z2 and Z3 are single bonds.
(4) A difluorovinyl compound as described in the above item (1), wherein either one of A1 and A2 is 1,3-dioxane-2,5-diyl, and the other is 1,4-cyclohexylene; A3 is 1,4-cyclohexylene; and A4, Z1, Z2 and Z3 are single bonds.
(5) A difluorovinyl compound as described in the above item (1), wherein either one of A1, A2 and A3 is 1,3-dioxane-2,5-diyl, and the remaining two are 1,4-cyclohexylenes; A4 is 1,4-cyclohexylene; and Z1, Z2 and Z3 are single bonds.
(6) A difluorovinyl compound as described in the above item (1), wherein A1 is 1,3-dioxane-2,5-diyl; A2 is 1,4-cyclohexylene; Z1 is xe2x80x94(CH2)2xe2x80x94 or xe2x80x94(CH2)4xe2x80x94; and A3, A4, Z2 and Z3 are single bonds.
(7) A difluorovinyl compound as described in the above item (1), wherein either one of A1 and A2 is 1,3-dioxane-2,5-diyl, and the other is 1,4-cyclohexylene; A3 is 1,4-cyclohexylene; either one of Z1 and Z2 is xe2x80x94(CH2)2xe2x80x94 or xe2x80x94(CH2) 4-, and the other is a single bond; and A4, Z1, Z2 and Z3 are single bonds.
(8) A difluorovinyl compound as described in the above item (1), wherein either one of A1, A2 and A3 is 1,3-dioxane-2,5-diyl, and the remaining two are 1,4-cyclohexylenes; A4 is 1,4-cyclohexylene; and either one of Z1, Z2 and Z3 is xe2x80x94(CH2)2xe2x80x94 or xe2x80x94(CH2)4xe2x80x94, and the remaining two are single bonds.
(9) A liquid crystal composition comprising at least one difluorovinyl compound as described in any of the above items (1) to (8).
(10) A liquid crystal composition comprising at least one difluorovinyl compound as described in any of the above items (1) to (8) as a first component and at least one compound selected from the group consisting of compounds represented by Formulas (2), (3) and (4) as a second component: 
wherein R1 represents an alkyl group having 1 to 10 carbon atoms, in which optional xe2x80x94C2xe2x80x94 in this alkyl group may be replaced by xe2x80x94Oxe2x80x94 or xe2x80x94C=CHxe2x80x94, but xe2x80x94Oxe2x80x94 is not adjacent to each other and in which optional H in this group may be substituted with F; X1 represents F, Cl, xe2x80x94OCF3, xe2x80x94OCF2H, xe2x80x94CF3, xe2x80x94CF2H, xe2x80x94CFH2, xe2x80x94OCF2CF2H or xe2x80x94OCF2CFxe2x95x90CF3; L1 and L2 each independently represent H or F; Z4 and Z5 each independently represent xe2x80x94(CH2)2xe2x80x94, xe2x80x94(CH2)4xe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94CF2Oxe2x80x94, xe2x80x94OCF2xe2x80x94, xe2x80x94C=CHxe2x80x94 or a single bond; a ring B and a ring C each independently represent 1,4-cyclohexylene, 1,3-dioxane-2,5-diyl or 1,4-phenylene in which H may be substituted with F; and a ring D represents 1,4-cyclohexylene or 1,4-phenylene in which H may be substituted with F.
(11) A liquid crystal composition comprising at least one difluorovinyl compound as described in any of the above items (1) to (8) as the first component and at least one compound selected from the group consisting of compounds represented by Formulas (5) and (6) as a second component: 
wherein R2 and R3 each independently represent an alkyl group having 1 to 10 carbon atoms, in which optional xe2x80x94C2xe2x80x94 in these alkyl groups may be replaced by xe2x80x94Oxe2x80x94 or xe2x80x94C=CHxe2x80x94, but xe2x80x94Oxe2x80x94 is not adjacent to each other and in which optional H in these alkyl groups may be substituted with F; X2 represents xe2x80x94CN or xe2x80x94Cxe2x89xa1Cxe2x80x94 CN; a ring E represents 1,4-cyclohexylene, 1,4-phenylene, 1,3-dioxane-2,5-diyl or pyrimidine-2,5-diyl; a ring F represents 1,4-cyclohexylene, 1,4-phenylene in which H may be substituted with F or pyrimidine-2,5-diyl; a ring G represents 1,4-cyclohexylene or 1,4-phenylene; Z6 represents xe2x80x94(CH2)2xe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94CF2Oxe2x80x94, xe2x80x94OCF2xe2x80x94 or a single bond; L3, L4 and L5 each independently represent H or F; and a, b and c each independently represent 0 or 1.
(12) A liquid crystal composition comprising at least one difluorovinyl compound as described in any of the above items (1) to (8) as the first component and at least one compound selected from the group consisting of compounds represented by Formulas (7), (8) and (9) as a second component: 
wherein R4 and R5 each independently represent an alkyl group having 1 to 10 carbon atoms, in which optional xe2x80x94C2xe2x80x94 in this alkyl group may be replaced by xe2x80x94Oxe2x80x94 or xe2x80x94C=CHxe2x80x94, but xe2x80x94Oxe2x80x94 is not adjacent to each other and in which optional H in this alkyl group may be substituted with F; a ring I and a ring J each independently represent 1,4-cyclohexylene or 1,4-phenylene; L6, L7, L8 and L9 each independently represent H or F, but all are not H at the same time; and Z7 and Z8 each independently represent xe2x80x94(CH2)2xe2x80x94, xe2x80x94COOxe2x80x94 or a single bond.
(13) A liquid crystal composition comprising at least one difluorovinyl compound as described in any of the above items (1) to (8) as the first component, at least one compound selected from the group consisting of the compounds represented by Formulas (2), (3) and (4) as the second component and at least one compound selected from the group consisting of compounds represented by Formulas (10), (11) and (12) as a third component: 
wherein R6 and R7 each independently represent an alkyl group having 1 to 10 carbon atoms, in which optional xe2x80x94C2xe2x80x94 in this alkyl group may be replaced by xe2x80x94Oxe2x80x94 or xe2x80x94C=CHxe2x80x94, but xe2x80x94Oxe2x80x94 is not adjacent to each other and in which optional H in this alkyl group may be substituted with F; a ring K, a ring M and a ring N each independently represent 1,4-cyclohexylene, pyrimidine-2,5-diyl or 1,4-phenylene in which H may be substituted with F; and Z9 and Z10 each independently represent xe2x80x94Cxe2x89xa1Cxe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94(CH2)2xe2x80x94, xe2x80x94Cxe2x80x94Cxe2x80x94 or a single bond.
(14) A liquid crystal composition comprising at least one difluorovinyl compound as described in any of the above items (1) to (8) as the first component, at least one compound selected from the group consisting of the compounds represented by Formulas (5) and (6) as the second component and at least one compound selected from the group consisting of the compounds represented by Formulas (10), (11) and (12) as the third component.
(15) A liquid crystal composition comprising at least one difluorovinyl compound as described in any of the above items (1) to (8) as the first component, at least one compound selected from the group consisting of the compounds represented by Formulas (7), (8) and (9) as the second component and at least one compound selected from the group consisting of the compounds represented by Formulas (10), (11) and (12) as the third component.
(16) A liquid crystal composition comprising at least one difluorovinyl compound as described in any of the above items (1) to (8) as the first component, at least one compound selected from the group consisting of the compounds represented by Formulas (2), (3) and (4) as the second component, at least one compound selected from the group consisting of the compounds represented by Formulas (5) and (6) as the third component and at least one compound selected from the group consisting of the compounds represented by Formulas (10), (11) and (12) as a fourth component.
(17) A liquid crystal composition comprising at least one liquid crystal composition as described in any of the items (9) to (16) and further comprising at least one optically active compound.
(18) A liquid crystal display constituted with the liquid crystal composition as described in any of the items (9) to (17).
(19) A difluorovinyl compound represented by Formula (13): 
wherein A3 and A4 each independently represent 1,4-cyclohexylene in which optional xe2x80x94CH2xe2x80x94 may be replaced by xe2x80x94Oxe2x80x94, 1,4-phenylene in which optional H may be substituted with halogen, and a single bond; Z2 and Z3 each independently represent a single bond, xe2x80x94(CH2)2xe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94, (CH2)4xe2x80x94, xe2x80x94O(CH2)3xe2x80x94 or (CH2)3O; and n represents 0 or an integer of 1 to 10.
The compound of the present invention represented by Formula (1) is a dicyclic to tetracyclic compound that has a hetero ring having an oxygen atom and a difluorovinyl group together in a skeleton.
A compound having a difluorovinyl group is disclosed in, for example, Japanese Patent Application Laid-Open No. 308239/1989. However, a compound having a skeleton containing a hetero ring such as a dioxane ring and a difluorovinyl group at the same time as is the case with the present invention is not described therein. Also, a compound formed from a dioxane ring and a difluorovinyloxy group is described in, for example, U.S. Pat. No. 5,997,766. However, reference to description in which the characteristics of the above compound are introduced in Abstract in Freiburger Arbeitstagung Flussigkristalle held in Mar. 25 through 27, 1998 shows that a problem is involved in a chemical stability thereof. Further, a compound having a dioxane ring and a difluorovinyloxy group at the same time is described in EP 593997, but it is shown merely as a synthetic intermediate, and usefulness thereof as a liquid crystalline compound as is the case with the present invention is not shown.
The liquid crystalline compound of the present invention is characterized not only by that it is physically and chemically very stable under conditions on which a display is used but also that it has a wide liquid crystal phase temperature range, good solubility in a liquid crystal composition even at low temperature, low viscosity, suitable dielectric anisotropy and a large elastic constant ratio K33/K11. Among the molecule-structural elements, the ring structure and the structure of the bonding group or the side chain are suitably selected, whereby the desired physical values can optionally be controlled. The preferred compounds shall be shown below. 
(Y1 and n are the same as those described above).
Among the compounds described above, the dicyclic compounds of (1-1) to (1-4) have positive dielectric anisotropy and show a large elastic constant ratio K33/K1. and low viscosity. When used for a liquid crystal composition, these characteristics are reflected on the characteristics of the liquid crystal composition, and it has the advantage that only the viscosity is reduced without particularly lowering the clearing point. The tricyclic compounds of (1-5) to (1-13) have the same characteristics as those of the dicyclic compounds, and when used for a liquid crystal composition, the clearing point can be set up high. Further, the tetracyclic compounds of (1-14) to (1-22) have a high clearing point and a positive dielectric anisotropy and show a large elastic constant ratio K33/K11. They have a relatively low viscosity though they are tetracyclic compounds and can be increased in a clearing point while maintaining the viscosity of the liquid crystal composition.
Further, the following ones can be given as preferred Y1 in the compounds described above.
It includes an alkyl group having 1 to 10 carbon atoms, an alkoxy group, an alkoxyalkyl group, an alkenyl group, an alkenyloxy group, an alkenyloxyalkyl group and an alkyloxyalkenyl group. Among them, the particularly preferred groups include methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, methoxy, ethoxy, propoxy, butoxy, pentyloxy, hexyloxy, heptyloxy, octyloxy, methoxymethyl, ethoxymethyl, propoxymethyl, butoxymethyl, methoxyethyl, ethoxyethyl, propoxyethyl, methoxypropyl, ethoxypropyl, propoxypropyl, vinyl, 1-propenyl, 2-propenyl, 1-butenyl, 2-butenyl, 3-butenyl, 1-pentenyl, 2-pentenyl, 3-pentenyl, 4-pentenyl, 2-propenyloxy, 2-butenyloxy, 2-pentenyloxy, 4-pentenyloxy, methoxy-1-propenyl, methoxy-1-pentenyl methoxy-3-pentenyl and so on. The compounds in which Y1 is an optically active group are particularly useful as a chiral dopant. Use thereof can prevent reverse twist domains from being produced.
Further, the compounds of the present invention show the same characteristics also when they are substituted in structural atoms thereof with isotopes, and therefore they are preferred as well.
The liquid crystal composition of the present invention shall be explained below. The liquid crystal composition of the present invention preferably contains 0.1 to 99.9% by weight of at least one compound represented by Formula (1) in order to allow excellent characteristics to be revealed, and a content thereof is more preferably 1 to 80% by weight and further preferably 1 to 60% by weight.
The liquid crystal composition provided by the present invention may comprise only the first component containing at least one liquid crystalline compound represented by Formula (1), and preferred is the compound comprising as the second component, in addition thereto, at least one compound (hereinafter referred to as a second A component) selected from the group consisting of the compounds represented by Formulas (2), (3) and (4) described above and/or at least one compound (hereinafter referred to as a second B component) selected from the group consisting of the compounds represented by Formulas (5) and (6). Further, the composition can contain as well at least one compound selected from the group consisting of the compounds represented by Formulas (10), (11) and (12) as the third component for the purpose of controlling a threshold voltage, a liquid crystal temperature range, optical anisotropy, dielectric anisotropy and viscosity.
Further, the respective components of the liquid crystal composition used for the present invention have no large difference between the physical characteristics, and therefore they may be analogues comprising isotopic elements of the respective elements.
In the second A component described above, capable of being given respectively are the compounds of formulas (2-1) to (2-9) as suitable examples of the compound represented by Formula (2), the compounds of formulas (3-1) to (3-97) as suitable examples of the compound represented by Formula (3) and the compounds of formulas (4-1) to (4-33) as suitable examples of the compound represented by Formula (4). 
(in the formulas, R1 and X1 are the same as those described above).
The compounds represented by these Formulas (2) to (4) show a positive dielectric anisotorpy and is very excellent in heat stability and chemical stability, sot hat it is used primarily for a liquid crystal composition for TFT. When preparing a liquid crystal composition for TFT, a sue amount of the above compound falls suitably in a range of 0.1 to 99.9% by weight, preferably 10 to 97% by weight and more preferably 40 to 95% by weight based on the whole weight of the liquid crystal composition. The compounds represented by Formulas (10) to (12) may further be added for the purpose of controlling the viscosity.
Next, in the second B component described above, the compound of formulas (5-1) to (5-58) and (6-1) to (6-3) can be given as suitable examples of the compounds represented by Formulas (5) to (6). 
(in the formulas, R2, R3 and X2 are the same as those described above).
The compounds represented by these Formulas (5) and (6) have a positive dielectric anisotropy, and a value thereof is very large, so that they are used mainly for the liquid crystal compositions for STN and TN. These compounds are used as a composition component particularly for the purpose of reducing a threshold voltage. Also, they are used for the purposes of controlling the viscosity and the optical anisotropy and expanding the liquid crystal phase temperature range and also for the purpose of improving the steepness. When preparing a liquid crystal composition for STN or TN, a use amount of the compounds represented by the Formulas (5) and (6) can be applied in a range of 0.1 to 99.9% by weight. A third component described later can be mixed for the purpose of controlling the threshold voltage, the liquid crystal phase temperature range, the optical anisotropy, the dielectric anisotropy and viscosity.
When a liquid crystal composition having a negative dielectric anisotropy which is used for a vertical aligning mode (VA mode) is prepared as the liquid crystal composition of the present invention, preferred is the composition mixed with at least one compound (hereafter referred to as a second C component) selected from the group consisting of the compound represented by Formulas (7) to (9). Compounds of formulas (7-1) to (7-3), (8-1) and (9-1) to (9-3) can be given respectively as suitable examples of the compounds represented by Formulas (7) to (9) in the second C component. 
(in the formulas, R4 and R5 are the same as those described above).
The compounds represented by Formulas (7) to (9) are compounds having a negative dielectric anisotropy. The compound represented by Formula (7) is a dicyclic compound and therefore is used mainly for the purpose of controlling the threshold voltage, the viscosity or the dielectric anisotropy. The compound represented by Formula (8) is used not only for the purpose of expanding the nematic range by elevating the clearing point but also for the purpose of reducing the threshold voltage and increasing the optical anisotropy.
The compounds represented by Formulas (7) to (9) are used mainly for the liquid crystal composition for a VA mode having a negative dielectric anisotropy. If the use amount thereof is allowed to grow large, the composition is reduced in a threshold voltage but increased in viscosity, and therefore it; is preferably used in a smaller amount as long as a required value of the threshold voltage is satisfied. However, an absolute value of the dielectric anisotropy is 5 or less, and therefore the use amount of smaller than 40% by weight makes it impossible in a certain case to carry out voltage driving. A use amount of the compounds represented by Formulas (7) to (9) is preferably 40% by weight or more, more preferably 50 to 95% by weight when preparing the composition for a VA mode.
Further, the compounds represented by Formulas (7) to (9) are mixed in a certain case with the liquid crystal composition having a positive dielectric anisotropy for the purpose of controlling the elastic constant and a voltage transmission curve of the composition. In this case, a use amount of the compounds represented by Formulas (7) to (9) is preferably 30% by weight or less.
In the third component for the liquid crystal composition of the present invention, compounds of formulas (10-1) to (10-11), (11-1) to (11-12) and (12-1) to (12-6) can be given respectively as suitable examples of the compounds represented by Formulas (10) to (12). 
(in the formulas, R6 and R7 are the same as those described above).
The compounds represented by Formulas (10) to (12) are compounds which have a small absolute value of dielectric anisotropy and which are close to neutrality. The compound represented by Formula (10) is used mainly for the purpose of controlling the viscosity or the optical anisotropy. Further, the compounds represented by Formulas (11) and (12) are used for the purpose of broadening the nematic range by elevating the clearing point or the purpose of controlling the optical anisotropy.
If a use amount of the compounds represented by the Formulas (10) to (12) is increased, the liquid crystal composition is elevated in a threshold voltage and reduced in viscosity, and therefore it is used preferably in a large amount as long as a required value of a threshold voltage of the liquid crystal composition is satisfied. When preparing the liquid crystal composition for TFT, a use amount of the compounds represented by Formulas (10) to (12) is preferably 40% by weight or less, more preferably 35% by weight or less. Further, when preparing the liquid crystal composition for STN or TN, a use amount of the compounds represented by Formulas (10) to (12) is preferably 70% by weight or less, more preferably 60% by weight or less.
The liquid crystal composition provided according to the present invention preferably contains at least one of the liquid crystalline compounds represented by Formula (1) in a proportion of 0.1 to 99% by weight in order to allow excellent characteristics to be revealed.
The above liquid crystal composition is usually prepared by a publicly known method, for example, a method in which various components are dissolved at high temperatures. Further, suitable additives are added if necessary, whereby the liquid crystal composition is improved according to intended uses and is optimized. Such additives are well known by a person averagely skilled in the art and described in detail in literatures. Usually, added is a chiral dopant having an effect of inducing a spiral structure of liquid crystal to control a required distortion angle and prevent inverse distortion. The following optically active compounds can be given as examples of the chiral dopant used in this case. 
Usually, in the liquid crystal composition of the present invention, these optically active compounds are added to control a pitch in distortion. The pitch in distortion is preferably controlled in a range of 40 to 200 xcexcm in the case of the liquid crystal compositions for TFT and TN. In the case of the liquid crystal composition for STN, it is preferably controlled in a range of 6 to 20 xcexcm. Further, in the case of the liquid crystal composition for a bistable TN mode, it is preferably controlled in a range of 1.5 to 4 xcexcm. Two or more kinds of the optically active compound may be added for the purpose of controlling a temperature dependency of the pitch.
The liquid crystal composition of the present invention can also be used as a liquid crystal composition for a G-H mode by adding a dichromatic dye such as a merocyanine base, a styryl base, an azo base, an azomethine base, an azoxy base, a quinophthalone base, an anthraquinone base and tetrazine base. The liquid crystal composition according to the present invention can also be used as a liquid crystal composition for a birefrigence-controlling (ECB) mode and a DS mode as well as NCAP prepared by micro-capsulizing nematic liquid crystal and polymer dispersion mode liquid crystal display (PDLCD) prepared by forming a three-dimensional network polymer in the liquid crystal, for example, a polymer network liquid crystal display (PNLCD).
The compounds (1) and (13) of the present invention can easily be produced by using conventional organic synthetic chemical method. They can readily be synthesized by suitably selecting and combing known reactions described in publications and magazines such as, for example, Organic Synthesis (John Wiley and Sons), Organic Reactions (John Wiley and Sons), Comprehensive Organic Synthesis (Pergamon Press) and New Experimental Chemistry Course (Maruzen).
To be specific, a difluorovinyl group can be introduced through a route shown below. That is, an aldehyde derivative (21) is reacted with sodium chlorodifluoroacetate and triphenyl phosphine in N,N-dimethylformamide (hereinafter abbreviated as DMF) and diethylene glycol dimethyl ether, whereby the compound (1) can be obtained: 
(in the formulas, A1, A2, A3, A4, Z1, Z2, Z3 and n are the same as those described above).
Further, the synthetic intermediate (13) can be synthesized as well through a route which is similar to that shown above. That is, an aldehyde derivative (31) is reacted with sodium chlorodifluoroacetate and triphenyl phosphine in DMF and diethylene glycol dimethyl ether, whereby the compound (13) can be obtained: 
(in the formulas, A3, A4, Z2 and Z3 are the same as those described above).
The synthetic intermediate (13) is reacted with triphenylphophonium halide (32) in the same manner as described above in an ether base solvent such as THF and diethyl ether in the presence of a base such as sodium methylate, potassium t-butoxide (t-BuOK) and butyl lithium and then dehydrated by virtue of an action of a mineral acid such as hydrochloric acid and sulfuric acid or an organic acid such as formic acid and p-toluenesulfonic acid, whereby an aldehyde compound (34) is obtained. The compound (34) is reacted with a diol compound (35) by virtue of an action of a mineral acid such as hydrochloric acid and sulfuric acid or an organic acid such as formic acid and p-toluenesulfonic acid, whereby a dioxane ring can be introduced as shown in a compound (36): 
(in the formulas, A3, A4, Z2 and Z3 are the same as those described above, and Hal is Cl, Br or I).
The liquid crystalline compound of the present invention thus obtained is physically and chemically very stable under conditions on which a display is used. Further, it shows such characteristics that it has a wide liquid crystal phase temperature range, a good solubility in a liquid crystal dielectric anisotropy and large elastic constant ratio K33/K11, and it is very excellent as a structural component for a liquid crystal composition suited to various display modes. Further, the synthetic intermediate is very useful in synthesizing the liquid crystalline compound of the present invention.